In plants for the manufacture of polymer and/or the conversion of polymer to granules or finished articles, it is known to transport polymer particles, such as powders, beads or granules, pneumatically. These polymer particles are transported with the aid of a carrier gas in a pipeline consisting of a system of pipes characterized by a constant cross-section and more particularly by a circular section of constant diameter. However, during transport of the polymer, the formation of threads or filaments, disturbing the transport and the conversion of this polymer, is observed inside the pipelines. The formation of threads or filaments is essentially due to degradation or crumbling of the polymer particles. This degradation or crumbling takes place when the particles rub against one another or against the walls of the pipelines, with incipient melting of the polymer, especially in zones where the flow can be of the laminar type. These phenomena are generally observed when hot polymer particles are transported or when the particles are transported with the aid of a hot carrier gas.
To minimize the degradation or crumbling of the polymer particles during their transport, it has already been proposed to use pipes having a rough internal surface or having notches formed in their inner wall. In particular, the pipes can have, on their internal surface, circular or helical notches which can be made with the aid of a special device moving inside these pipes. It is thus impossible to produce such pipes in an already existing plant. Furthermore, during transport of the polymer, the notches can fill with polymer particles and can therefore lose their effect on the transport of the particles. In addition, the polymer transported in such pipes can be contaminated by another polymer, of a different quality, which has previously been transported in these pipes.